This invention relates to a method for producing a master pattern, or more in particular to a method for producing a master pattern used for manufacture of the phosphor screen of the color picture tube.
A phosphor screen of a color picture tube in which the spaces around circular, rectangular or striped red, blue and green phosphor dots are filled with such light-absorbing material as carbon is well known. The color picture tube having this type of phosphor screen is generally called a black matrix color picture tube or black surround color picture tube and is presently most widely used due to advantageous features including a bright picture and high contrast.
As apparent from the U.S. Pat. No. 3,558,310, the processes of manufacture of the phosphor screen of the black matrix color picture tube are highly complicated and so are eagerly required to be simplified.
First, a conventional method for producing the phosphor screen of the black matrix color picture tube will be briefly described below.
As shown in FIG. 1, a shadow mask 3' is mounted on a glass face panel 1 having an internal surface coated with photo-resist or phosphor slurry 2 for forming a black matrix, and the assembly is placed on an exposure mount A. In order to harden the photo-resist at the positions of red, blue and green or to apply the phosphors of the corresponding colors to those positions exposure and development are effected by the use of three spot light sources 4, 4' and 4" through a compensating lens 5 and the shadow mask 3'.
Thus, production of a black matrix requires three exposures and one development, and production of phosphor dots requires three exposures and three developments. At each time of exposures and developments, the shadow mask is mounted and removed. The resulting inconvenience is the need for a multiplicity of exposure mounts, and multiple repetitions of a series of complicated processes including application and drying of photo-resist or phosphor slurry, the mounting of a shadow mask exposure, removal of the shadow mask and development. Further, for lack of interchangeability the conventional shadow mask, used for forming the phosphor screen, is incorporated into the color picture tube, so that the face panel and the shadow mask is handled as a couple from the first to the last of the above-mentioned complicated series of processes, resulting in great practical inconveniences.
For simplifying these complicated processes to any degree, it is certainly effective to use, as an alternative to the conventional shadow mask, "interchangeable shadow masks" usable interchangeably which have a multiplicity of apertures formed at completely identical positions. Several types of interchangeable mask and the method of production thereof are suggested in the U.S. Pat. Nos. 3,794,873 and 3,909,928 and the Japanese Patent Laid-Open Nos. 16068/72, 7021/71 and 108570/76.
No new method for producing a color picture tube using interchangeable shadow masks nor a method for producing a color picture tube fully utilizing the advantages of the interchangeable shadow masks have so far been developed before the present invention.